I want to start writing and directing and send my short films to international festivals. .
My suggestion:
Then write and direct. There's no reason to spend exorborant amounts of time learning camera tech, and practicing operating skills if your goal is to be a writer/director.
Start looking around for other aspiring filmmakers and when you meet one with whom you get along who starts conversations with phrases like "I want to shoot and light films, and I just picked up (insert camera, camera accessory, or lighting toy here) the other day. I'm totally dying to use it, but I'm looking for a writer/director to hook up with."
Then the two of you learn EVERYTHING you can about producing and the logistics of shooting. You worry about the writing and the directing, let him/her worry about what camera to use, what lenses are good, what support gear won't break or fail on you or otherwise just generally suck, and so on. And that's just scratching the surface of camera without going into lighting or sound.
Even better, take your camera budget, buy some sound gear, and find an aspiring shooter with camera gear. That way you can have the best of both worlds, without having to shell out for all of the gear.
I know this advice flies in the face of a lot of indie workflow, but if the goal is to write and direct films with the intent of making it a career there are other ways to get there.
TLDR version:
If you want to write and direct, then write and direct. It's good to know the language of the camera, but you don't need to spend energy on endless technical comparisons. Find an aspiring DP and let them do that. Concentrate on story, dialogue, character, blocking, and so on.
Just an alternate opinion.